Electroacoustical transducer

ABSTRACT

A reversible electroacoustical transducer, having a circular configuration generated about a longitudinal axis, is disclosed as incorporating a backing plate disposed normal to said longitudinal axis. A first plastic washer is disposed around said longitudinal axis and spatially disposed from said backing plate. A trio of piezoelectric ceramic energy converter rings, having similar outside diameters and different inside diameters, is spatially disposed around and along said longitudinal axis. Another plastic washer is disposed around said longitudinal axis and spatially disposed from said trio of piezoelectric ceramic energy converter rings. And, with the exception of the aforesaid backing plate, all of the aforesaid elements are encapsulated and potted in a polyurethane material, the latter of which is bonded to said backing plate.

[ 1 Nov. 25, 1975 1 ELECTROACOUSTICAL TRANSDUCER [75] Inventors: Rufus L. Cook, Panama City; James H. Elkins, Lynn Haven, both of Fla,

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

22 Filed: Aug. 12,1974

[21] Appl. No.:496,498

Primary Examiner-Mark O. Budd Attorney, Agent, or Firm Richard S. Sciascia', Don D, Doty; Harvey A, David [57] ABSTRACT A reversible electroacoustical transducer, having a circular configuration generated about a longitudinal axis, is disclosed as incorporating a backing plate disposed normal to said longitudinal axis A first plastic washer is disposed around said longitudinal axis and spatially disposed from said backing plate. A trio of piezoelectric ceramic energy converter rings, having similar outside diameters and different inside diameters, is spatially disposed around and along said longi tudinal axis Another plastic washer is disposed around said longitudinal axis and spatially disposed from said trio of piezoelectric ceramic energy con verter rings. And, with the exception of the aforesaid backing plate, all of the aforesaid elements are encap sulated and potted in a polyurethane material, the latter of which is bonded to said backing plate,

22 Claims, 11 Drawing Figures US. Patent Nov. 25, 1975 Sheet 2 of2 3,922,572

o o m H m mum NOE ELECTROACOUSTICAL TRANSDUCER STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefor.

FIELD OF THE INVENTION The present invention, in general, relates to energy converters and, in particular, is a reversible electroacoustical transducer for converting electrical energy into acoustical energy proportional thereto and vice versa. In even greater particularity, the subject invention is an electroacoustical transducer having doughnut-like or other acoustical radiation and response patterns which are substantially uniform in configuration about an axis normal thereto.

BACKGROUND OF THE INVENTION Heretofore, numerous electroacoustical transducers of various and sundry geometrical configurations and incorporating one or more reversible piezoelectric elements have been used for projecting acoustical energy in resonse to electrical energy excitation and vice versa for many different purposes, especially in conjunction with sonars. Accordingly, the electroacoustical transducer art is so crowded that it would be impractical, if not impossible, to described each one in sufficient detail for the purpose of setting a predicate for the instant invention. Suffice to say, then, that it is well known to employ piezoelectric ceramic elements, either individually or in concert, as a generator and/or receiver of acoustical or sonic energy within many different types of environmental mediums, and especially in water, sea water, and the like. Moreover, for many practical purposes, the electroacoustical transducers of the prior art are quite satisfactory, although, to date, they have not reached the stage of development where they are perfect, even for some particular operational circumstance. Thus, for example, in many instances the total structures thereof are such that they may be cumbersome and unwieldy at times, the resolution and fidelity thereof leaves something to be desired, the bandwidths are too narrow because their frequency response curves are not substantially flat (or are at least not flat enough for some given purpose) and the functional power levels are too low for optimum operation.

Because the present invention overcomes some of the disadvantages of the prior art, it advances the state of the art to some degree, thereby providing an improvement which is quite desireable at the present time. Therefore, without further belaboring the prior art inasmuch and much of it is obviously already known to the artisans working in the research frontiers thereof the subject invention will now be discussed briefly from the structural and operational standpoints.

SUMMARY OF THE INVENTION As suggested above, the present invention overcomes some of the disadvantages of the prior art electroacoustical transducers. This is so, because of the uniquely structured combination of elements incorporated therein, with each thereof precisely dimensioned (relatively speaking), so as to perform with optimum interaction with its co-acting elements. Furthermore, the structure thereof has been so simplified that otherwise LII spurious vibrations and adverse electrical and acoustical effectations are reduced to an extent ostensively unobtainable to this time. As a matter of fact, for its intended purpose, the essence of the invention is so simple that the structural and operational significance thereof is difficult to comprehend unless one has access to the calibration and test results thereof. the latter of which will be discussed in greater detail subsequently.

Although other structure is or may be involved, the crux of the invention appears to lie in three accurately dimensioned painted, energy converter rings of similar outside diameters and different inside diameters, and which may be of substantially identical thickness that are geometrically held in predetermined optimum spaced relationships with each other between a pair of non-piezoelectric rings of different inside diameters and outside diameters that are larger than the outside diameters of the aforesaid energy converter rings by a unitary acoustically clear support member having a durometer of thirty-five to forty. Such simple but unique structure, of course, causes the desired objectives of invention to be effected.

it is, therefore, an object of this invention to provide an improved electroacoustical transducer.

Another object of this invention is to provide a relatively small, high power, broadband, reversible electroacoustical transducer that will function with improved operational resolution, fidelity, and efficiency within numerous environmental mediums, including water, sea water, and the like.

Still another object of this invention is to provide an easily handled electroacoustical transducer that will operate over the frequency range of seven to 15 kilohertz.

A further object of this invention is to provide a totally polyurethane encapsulated electroacoustical transducer.

A further object of this invention is to provide a broadband electroacoustical transducer that, for many practical purposes, is more distortion-free than those of the prior art.

Another object of this invention is to provide a transducer that will lend itself to the transmission of linear frequency modulated signals.

Another object of this invention is to provide a transducer that will simulate ocean vessel noises.

Still another object of this invention is to provide a transducer that minimizes the effects of constructive and destructive interference of sonar signals.

A further object of the present invention is to provide an improved transducer having radiation and response patterns which are useful for many underwater purposes and in many underwater applications.

Another object of this invention is to provide an improved method of constructing an electroacoustical transducer.

Still another object of this invention is to provide an improved method and means for broadcasting acoustical energy having a substantially disc-like. doughnutlike, or other radiation patterns and for receiving and responding to a similar acoustical energy pattern.

Another object ofthis invention is to provide an electroacoustical transducer that is easilyand economically manufactured, stored, operated, maintained. and transported.

Other objects and many of the attendant advantages will be readily appreciated as the subject invention becomes better understood by referenee to the following detail description. when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is an elevational view. predominantly in crosssection but with parts broken away. of a preferred embodiment of the electroacoustical transducer constituting the invention;

FIG. 2 is an elevational crosssectional view (with parts broken away) of another preferred embodiment of the electroacoustical transducer constituting the in vention;

FIG. 3 is an elcvational view. partially in cross-section. which illustrates a representative transducer construction mold for potting the preferred embodiments of the invention depicted in FIGS. I and 2;

FIG. 4 is an exemplary perspective view ofthe invention which shows that the preferred embodiments thereof may be round in configuration. as viewed from the top thereof;

FIG. 5 is an elevational view. partially in cross-section. of the subject transducer combined with other utilization apparatus in a projectile-like housing in such manner that it will transmit and receive acoustical energy in one doughnut-like or disc-like pattern that is normal to the longitudinal axis thereof;

FIG. 6 is an elevational view. partially in cross-section. of the subject transducer combined with other utilization apparatus in a projectile-like housing in such manner that it will transmit and receive acoustical energy in sidewardly and forwardly directions;

FIG. 7 is a schematic diagram of the electrical equivalents ofthe piezoelectric energy converter elements of the subject invention combined with the electrical equivalents of the cable. tuner. transformer and signal generator elements which are designed to provide optimum operation therewith;

FIGS. 8 and 9 are graphical representations ofthe radiation and reception patterns which emanate radially that is. perpendicular from the longitudinal axis of from and to the electroacoustical transducer consti tuting this invention. respectively. regardless ofthe preferred embodiment in which it is used;

FIG. 10 graphically illustrates the frequency response curve of the subject transducer during the transmitting mode of operation thereof; and

FIG. ll graphically illustrates the frequency response curve of the transducer constituting this invention during the receiving mode of operation thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I. there is shown the subject transducer 21 as having a base or backing plate 22, preferably made of aluminum or some other metal but, ofcourse. may be made of any non-resilient or resilient material required to optimize transducer operations during any given circumstances. In addition. backing plate 22 may be integrally or otherwise conventionally connected to a rearwardly extending body 23, which may have one or more bracing walls 24 incorporating holes 25 and 26 to allow the passage of electrical conductors or other apparatus therethrough.

For reasons which will be explained later but which are probably obvious from FIG. 1 ofthe drawing base plate 22 has a forwardly extending wall 27 containing a plurality of grooves 28 and 29 cut in the inside surface thereof.

Perhaps at this time. it would be noteworthy that. when viewed from the top or bottom. transducer 2! is round in configuration (as indicated in FIG. 4); however. it should be understood that any other suitable configuration may be the design therefor. if so desired.

Base plate 22 includes a plurality of internally threaded holes 31 and 32 in which externally threaded insulated electrical lugs 33 and 34 are screwed. so as to allow electricity conduction through said base plate 22, while maintaining sealed compartments 35 and 36 on both sides thereof. Base plate 22 and wall 24 also have holes 37 and 38 respectively extending through the center thereof. through which a bolt 39 extends along the longitudinal axis of the entire transducer, for rea sons which will be more fully explained subsequently.

At this time. it would appear to be worthy of note that. for convenience sake. it will be assumed that the physical attitude of the transducer shown in the draw ing is such that the top thereof (or front or forward po sition thereof) is located at the top of the drawing and the bottom thereof (or rear or rearward portion thereof) is located at the bottom of the drawing. Hence. the aforementioned longitudinal axis ofthe subject transducer may be seen to run up and down. al though in actual practice, the invention may be used in whatever physical disposition or attitude as is necessary for any given operational situation.

Setting on base plate 22 but extending upward therefrom is a plurality of cured polyurethane blocks or posts 40. the length of which is approximately 0.5 inch, and setting on the top of said plurality of blocks or posts 40 is an acoustically clear acryonitrile-butadinestyrene (ABS) washer 41 of 3.30 inches outside diameter and 3.00 inches inside diameter. And setting on the top surface of washer 41 is a plurality of cured polyurethane spacers 42 having a length of 0032. upon which a first lead zirconatelead titanate piezoelectric ceramic ring 43 polarized through its thickness dimension is disposed.

The specific dimensions of piezoelectric ring 43 of this preferred embodiment are important. The outside diameter thereof is 3.100 inches and the inside diameter thereof is 2.900 inches, thereby giving it a wall thickness of 0.100 inch. the thickness thereof (as measured along the transducer longitudinal axis direction) is 0.272 inch. Of course. ring 43 is preferably cut in the convention ceramic cutting manner. in order to have such accurate dimensions; nevertheless. other dimension refining procedures may be employed. if so desired.

Electroacoustical energy converter ring 43 has a pair of silver electrodes 44 and 46 respectively attached to the opposite sides thereof for the conventional purpose of effecting the electrical energization thereof when supplied with appropriate electrical current.

Sitting on the upper surface of electrode 46 of piezoelectric ring 43 is a second plurality of cured polyure thane spacers 47 having a length of 0.032. like spacers 42, and sitting on said spacers 47 is a second lead zir' conate-lead titanate piezoelectric ceramic ring 48 that is, likewise. polarized through its thickness dimension.

The specific dimensions of piezoelectric ring 48 are. like those of the aforementioned ring 43, of considerable importance. The outside diameter thereof is 3.100 inches. and the inside diameter thereof is 2.700 inches. thereby giving it a wall thickness of 0.200 inch. The thickness thereof which is measured along the longitu dinal axis of the transducer is 0.272 inch.

Electroacoustical energy converter ring 48 also has a pair of silver electrodes 49 and 51 respectively attached to the opposite sides thereof for timely effecting the electrical excitation thereof.

Sitting on the top surface of electrode 51 of ring 48 is a third plurality of cured polyurethane spacers S2 having a length of 0.032, and sitting on said spacers 47 is a third lead zirconatc-lead titanate piezoelectric ceramic ring 53 that is also polarized through its thickness dimension.

Like those of rings 43 and 48, the specific dimensions of piezoelectric ring 53 are of considerable importance. The outside diameter thereof is 3.l00 inches, and the inside diameter thereof is 2.800 inches, thereby making it have a wall thickness of 0.150 inch. The longitudinal thickness thereof as measured along the longitudinal axis of the transducer is 0.272 inch.

Electroacoustical energy converter ring 53 also has a pair of silver electrodes 54 and 55 respectively attached to the opposite sides thereof for effecting the electrical excitation thereof when electrical current is supplied thereto.

Still a fourth plurality of cured polyurethane spacers 57 sit on the top surface of electrode 54 of ring 53, and they each have a length of 0.032; and another acoustically clear acryonitrile-butadine-styrene (ABS) washer 58 sits on top of said spacers 57. Washer 58 has an outside diameter of 3.300 and an inside diameter of 2.800

inches.

From the foregoing, it may be seen that the spatial distance between the piezoelectric rings is 0.032 inch. Encapsulating all of the aforesaid elements located above the upper surface of backing plate 22 is an acoustically clear polyurethane housing 61 and potting 62 material. How such housing and potting structure is constructed in combination with their associated is very simple and will be discussed more fully below. Sufflee to say at this time, that they form outside wall 63 and upper wall 64, as well as occupy the space of compartment 35, including grooves 28 and 29. Of course, the occupying of grooves 28 and 29 effects a joint between potting 62 and the aforementioned extending body wall 27, the rigidity or resiliency of which is contingent upon the resiliency of potting material 62.

Although difficult to show and reference pictorially, a primer coat of paint preferably of Hysol P-l0 coats the external surface of all of the aforementioned transducer elements above the upper surface of backing plate 22; hence, it acts as a buffer between the outside surfaces thereof and the inside surfaces of the housing and potting material. For the sake of simplicity of disclosure, said paint is hereby referenced as primer paint 6S.

Mounted on the forward or upper end of transducer 21 is another aluminum or other matal plate 66 containing a center hole 67 through which the aforementioned bolt 38 extends. A nut 68 screwed tightly on bolt 38 very effectively holds transducer 21 in place between forward and backing plates 66 and 22. Of course, forward plate 66 may be integrally or otherwise connected to any other compatible apparatus 67 (not shown in detail in FIG. 1) required to be associated therewith, if operational circumstances so warrant.

Without intending to limit the scope of the subject invention, the preferred embodiment shows electroacoustical energy converter rings 43, 48, and 53 connected in electrical parallel by means of electrical conductors 71 and 72 connected between the various electrodes thereof and lugs 33 and 34, respectively. The other electrical leads 73 and 74 are or may be connected between said lugs 33 and 34 and any suitable utilization apparatus, such as, for example. sonar systems, or the like. Nevertheless. it should be understood that said electroacoustical energy converter rings may be connected in series, independently. in parallel. or any combination thereof, if so doing would optimize the operation of the subject transducer during any given operational circumstances.

Transducer 81, the preferred embodiment of the elcctroacoustical transducer of FIG. 2, is very similar to that of FIG. 1, except that it contains no mounting bolt extending therethrough, nor does it contain a forward plate at the top thereof. Hence, to simplify the discussion thereof, it should suffice to say that it contains a backing plate 82, washers 83 and 84, energy converter rings 85, 86, and 87, spacers 88, 89, 90, and 91, as well as acoustically clear housing 92 and potting 93. Also, obviously missing are posts similar to posts 39 of FIG. I.

The energy converter rings thereof are, likewise, shown to be connected in parallel by electrical conductors 94 and 95 which extend down through a hole 95 in backing plate 82. Of course, backing plate 82 may be integrally or otherwise attached to another object or body 96. Although forward wall 97 of polyurethane housing 92 is depicted as being flat, it may be round. streamlined, or have any other geometrical configuration, as long as it is acoustically clear.

All of the elements of the embodiment of FIG. 2 are preferably identical to similar ones of FIG. 1, as far as dimensions materials, configurations. and construction procedures are concerned.

FIG. 3 of the drawing is merely intended to show that either transducer 21 or 81 may be constructed by setting up all of the aforesaid elements thereof. respectively, in a mold 101 and then pouring heated liquid polyurethane material into the top thereof as schematically indicated by reference numeral I02 until it is filled to level I03, after which it is cooled or left to harden and become the aforementioned housings and pottings.

In the case of the embodiment of FIG. 2, part of said polyurethane material must be poured first and left to harden before assemblying the elements located above backing plate 82, with the remainder of the pouring thereof accomplished thereafter.

FIG. 4 has been included in the drawing to disclose the general external appearance of the embodiment of the invention shown in FIG. 1, but without bolt 38 or backing plate 22. Hence, reference numerals are used therein which are the same as used in FIG. 1 for similar parts. It is believed that the structure of FIG. 4 is selfevident as it is shown; however, if further illucidation is necessary, the reading of the discussion pertinent to FIG. 1 thereon should suffice to explain its structure quite adequately.

Referring now to FIG. 5, it is shown therein that transducer 21 of FIG. I may be incorporated in a substantially streamlined projectile shaped body which may contain various and sundry electronic utilization apparatus 111 and other apparatus I12 disposed, as desired, in rearward and forward compartments 113 and 114, respectively. Of course, the structures of compartments 113 and 114 may be of any par ticular designs as would optimize their being combined with electroacoustical transducer 21.

FIG. 6. like FIG. 5, shows another representative configuration in which the embodiment of FIGS. 1 and 2 may be incorported. as long as it is modified to extend forward polyurethane wall to have a forward extension I21 with rounded or streamlined nose I22, and a suit able nut I23 and passageway 124 included within extension 121 in such manner that bolt 39 may be screwed into it from the rear for the purpose of securely connecting transducer 21 to a rear compartment I25. Of course. as may readily be seen, rear compart ment 125 is designed to contain such electronic utilization apparatus as would be suitable for being combined with transducer 21 or 81.

Obviously, it would be well within the purview of one skilled in the art to design and construct the bodies. compartments. and the like. of the devices of FIGS. 5 and 6 in such manner as to effect the optimization thereof for any given purpose or ambient environmental medium. Accordingly. further discussion of specific structures thereof is deemed to be unnecessary.

THEORY OF OPERATION The theory of the operation of the embodiments of the electroacoustical transducers illustrated in FIGS. 1 and 2 will now be discussed briefly in conjunction with FIG. 7.

If. for instance. an electrical signal of known voltage and frequency. E is generated by any suitable generator I31 and supplied to the input primary winding of transformer I32, a voltage, E occurs which, in turn. is supplied via transmission cable 133 represented by inductor I34, resistor 135, and capacitor 136 to the electroacoustical piezoelectric elements I, II, and III. Because the total capacitive reactance of the piezoelectric elements is much greater than that of the transmission cable. when properly tuned. cable 133 serves primarily as a transmission line. and the attenuation ofthe electrical signal (E between transformer I32 and piezoelectric elements I. II, and III would be. for all practical purposes. negligible. Of course. the total capacitance of transmission line 133 and piezoelectric elements I. II. and Ill combined is effected by the proper adjustment of a variable inductance 137 connected in parallel with the secondary winding of transformer 132, to effectively compensate for the reactance inherently existing in elements I, II, and III, and discussed below.

The circuit parameters to be considered from the operational standpoint of the piezoelectric elements are Ra Ra and Ra which represent the radiation resistance encountered by ceramic elements I. II, and III. respectively; R R and R;,. which represent the internal motional resistance within piezoelectric elements I, II and III. respectively; L L and L;, which represent the effective inductance or masses of piezoelectric elements I. II. and III. respectively; C,, C and C which represent the effective capacitance or stiffness of the piezoelectric elements I. II, and III, respectively; C C and C which represent the total dielectric capacitance of piezoelectric elements, I, II. and III, respectively; and the mass loading of the polyurethane potting material on said piezoelectric elements I. II, and III. respectively.

It is well known that when the inductive reactance X and the capacitive reactance X,- of any given material in this case. involving the aforementioned R. L. and C terms are equal. a fundamental resonance fre quency may be observed therein. However. since in this particular instance the piezoelectric elements are encapsulated in a potting material. such potting material produces a mass loading effect or an additional inductance which must be taken into consideration. In other words. such potting materialss effective inductance causes the fundamental resonance of each piezoelectric ceramic element to shift in a downward direction. For example, piezoelectric element 43 of FIG. I, having a wall thickness of 0.100 inch. has its resonant fre' quency shifted down 4.88 KHz; piezoelectric element 48, having a wall thickness of 0.200 inch has its resonant frequency shifted down 0.32 KHz; and piezoelectric element 53, having a wall thickness of 0. l 50 inch. has its resonant frequency shifted down 2.63 KHz.

Hence, in view of the aforementioned dimensions. materials. parameters, and resonant frequency downshifts, it may readily be seen that a considerable number of factors have been taken into consideration in the construction of the electroacoustical transducer constituting this invention, in order to make it as perfect as possible for its intended use. Of course. such considerations also made it a relatively simple but unique device which obviously advances the state ofthe electroacous tical transducer art to some degree.

MODE OF OPERATION The subject invention will operate equally well in a transmitting mode of operation wherein it broadcasts acoustical energy in proportion to the electrical energy supplied thereto and a receiving mode of operation wherein it generates electrical energy in proportion to the acoustical energy received thereby. Therefore, if, for example. it is in the transmitting mode, it will broadcast an acoustical radiation pattern similar to that shown in FIG. 8; and if it is in the receiving mode, it will be responsive to the acoustical pattern illustrated in FIG. 9, with said two patterns being portrayed as if they were viewed from an extension of the longitudinal axis of the entire transducer. Obviously said two patterns are quite circular in shape for acoustical patterns and. hence, the structure which produces and is affected thereby constitutes an improvement, indeed.

Furthermore, as depicted in FIGS. 10 and 11, respectively. the transmitting and receiving frequency re sponse curves of the subject calibrated invention are. relatively speaking, quite flat, indeed. Thus. they. too, are indicative of the improved performance obtainable from the subject invention within the broadband frequency range of seven to fifteen kilohertz.

In any event. the subject transducer has been tested and found to be very efficient and have a high fidelity in underwater acoustical communication. things which have been desired for a long time.

While the transducer embodiment of FIG. I and the installation thereof in FIG. 5 tend to broadcast and re ceive doughnut shaped acoustical patterns similar to those shown in FIGS. 8 and 9, the transducer embodi ment of FIG. 2 and. say. a slightly modified version thereof shown in FIG. 6 tend to broadcast and receive semi-doughnut shaped acoustical patterns. with an elongated forward projection thereof corresponding to some extent to elongation of the forward polyurethane wall of the transducer. Thus. it may readily be seen that a variety of acoustical radiation and response patterns are possible. depending on the design of the forward end of the subject transducer. Obviously. it would be well within the purview of the artisan having the benefit of the teachings presented herewith to design the nose of the subject transducer to vary the forward acoustical pattern as desired.

METHOD OF CONSTRUCTION Because the resulting transducer constituting this invention may be exceedingly simple in its final form, the method of construction of it may not be readily apparent. Hence, it is outlined as follows for the exemplary embodiment of FIG. I:

1. Place backing plate 22 with lugs 33 and 34 in mold (like mold 103 of FIG. 3).

2. Arrange polyurethane posts 39 in upright position on upper surface of base plate 22.

3. Set washer 41 on posts 39.

4. Set spacers 42 on washer 39.

5. Set piezoelectric ring 43 on spacers 42.

6. Set additional rings and spacers like in step 5.

7. Set washer 58 on spacers 57.

8. Connect electrical leads between electrodes and lugs.

9. Insert bolt 38.

IO. Pour molten polyurethane potting material into the mold in such manner as to fill all space not occupied by the aforesaid elements and let set.

l l. Insert forward plate 65.

i2. Tighten nut 68 on bolt 38.

The above procedure may be modified so that the posts and spacers are of different materials from the polyurethane material used, or it may be modified to eliminate the posts entirely, so as to effect an embodiment similar to that shown in FIG. 2. However, it should be understood that, in either case, the posts, spacers, and potting material may be of the same that is, any appropriate material, which, in effect, makes said posts, spacers, potting material, and wall integral with each other or not in the final product, as preferred.

Obviously, other embodiments and modifications of the subject invention will readily come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing description and the drawings. It is, therefore, to be understood that this invention is not to be limited thereto and that said modifications and embodiments are intended to be included within the scope of the appended claims.

What is claimed is:

I. An electroacoustical transducer, comprising in combination:

a substantially rigid backing plate means, having at least one hole therethrough;

first washer means, having a predetermined inside diameter and a predetermined outside diameter, spatially disposed from said substantially rigid backing plate means;

a first ring-shaped piezoelectric means, having a first inside diameter and a first outside diameter, spatially disposed from said first washer means, for producing a first acoustical energy in proportional response to electrical energy supplied thereto and vice versa;

a second ring-shaped piezoelectric means. having a second inside diameter that is different from the first inside diameter of said first ring-shaped piezoelectric means and a scond outside diameter that is similar to the first outside diameter of said first ring-shaped piezoelectric means, for producing a second acoustical energy in proportional response to electrical energy supplied thereto and vice versa;

10 a third ring-shaped piezoelectric means, having a third inside diameter that is different from the first and second inside diameters of said first and second ring-shaped piezoelectric means and a third outside diameter that is similar to the first and second outside diameters of said first and second ringshaped piezoelectric means, for producing a third acoustical energy in proportional response to electrical energy supplied thereto and vice versa; second washer means having a predetermined inside diameter and a predetermined outside diameter, spatially disposed from said third ring-shaped piezoelectric means; electrical conductor means connected to said first, second, and third ring-shaped piezoelectric means and effectively passing through said at least one hole in said substantially rigid backing plate means for effecting the electrical connection thereof in a predetermined electrical circuit arrangement; plurality of polyurethane spacer means having inside diameters greater than the largest of the inside diameters of said first. second, and third ringshaped piezoelectric means and outside diameters smaller than the outside diameters thereof respectively disposed between adjacent ones of said first, second and third ring-shaped piezoelectric means and the aforesaid first and second washer means; and

acoustically clear means connected to each of the aforesaid means for effecting the holding thereof in the aforesaid spatial dispositions, respectively, for the containment thereof as an encapsulated unit of predetermined external geometrical configuration.

2. The device of claim 1, wherein said substantially rigid backing plate is a circular metallic backing plate having a plurality of holes therethrough.

3. The device of claim 1, wherein said substantially rigid backing plate is a circular aluminum backing plate having a plurality of holes therethrough.

4. The device of claim 1, wherein said first washer means has an inside diameter that is similar to the inside diameter of said first ring-shaped piezoelectric means and an outside diameter that is greater than the outside diameter thereof.

5. The device of claim 1, wherein said second ringshaped piezoelectric means has an inside diameter that is greater than the inside diameter of said first ringshaped piezoelectric means and has an outside diameter that is similar to the outside diameter thereof.

6. The device of claim I, wherein said first ringshaped piezoelectric means has an inside diameter of 3.000 inches and an outside diameter of 3.l00 inches.

7. The device of claim 1, wherein said second ringshaped piezoelectric means has an inside diameter of 2.900 inches and an outside diameter of 3.100 inches.

8. The device of claim 1, wherein said third ringshaped piezoelectric means has an inside diameter of 2.950 inches and an outside diameter of 3.100 inches.

9. The device of claim I, wherein the spaces between said first, second, and third spatially disposed ringshaped piezoelectric means are each 0.032 inches.

10. The device of claim I, wherein said third ringshaped piezoelectric means has an inside diameter that is smaller than the inside diameter of said second ringshaped piezoelectric means and larger than the inside diameter of said first ring-shaped piezoelectric means and an outside diameter that is similar to the outside diameter of said first and second ring-shaped piezoelecme means.

ll. The device of claim l, wherein each of said first, second, and third ring-shaped piezoelectric means comprises a lead zirconate-lead titanatc ceramic ring and a pair of silver electrodes connected to opposite side surfaces thereof.

T2. The device of claim I, wherein said second washer means has an inside diameter that is similar to the inside diameter of said third ring-shaped piezoelectric means and an outside diameter that is greater than the outside diameter thereof.

13. The device of claim I, wherein said acoustically clear means connected to each of the aforesaid means for effecting the holding thereofin the aforesaid spatial dispositions comprises a substantially resilient polyurethane material.

14. The device of claim 1, wherein said electrical conductor means comprises:

a pair of electrodes connected to opposite surface sides of each of said first, second, and third ringshaped piezoelectric means; and

a pair of electric wires respectively connected to each of the similar side electrodes of the pair of electrodes connected to opposite surface sides of each of said first, second, and third ring-shaped piezoelectric means for effecting the connection of said first, second, and third ring-shaped piezoelectric means in predetermined electrical circuit arrangement.

15. The device of claim 14, wherein said predetermined electrical circuit arrangement is in electrical parallel.

to. The device of claim 14, wherein said predetermined electrical circuit arrangement is in electrical series.

17. The device of claim 14, wherein said predetermined electrical circuit arrangement is such that said first, second. and third ring-shaped piezoelectric means are connected in electrically independent arrangement.

[8. The device of claim 1, wherein said acoustically clear means connected to each of the aforesaid means for effecting the holding thereof in the aforesaid spatial disposition is further disposed in such manner as to encapsulatc said first washer means, said first, second, and third ring-shaped piezoelectric means, said second washer means, and is connected to said substantially rigid backing plate means in such manner to be securely attached thereto as effectively an extension thereof.

19. The invention of claim 18, further characterized by a substantially rigid forwarding plate disposed in abutment with that external surface portion of the aforesaid acoustically clear encapsulating means that is adjacent to said second washer means; and means connected between said substantially rigid backing and forwarding plate means for holding said encapsulated first washer means, first, second, and third ring-shaped piezoelectric means, and said second washer means therebetween.

20. The invention of claim 19, wherein said means connected between said substantially rigid backing and forwarding plate means comprises at least one threaded bolt and a nut screwed on the end thereof.

21. The invention of claim 19, wherein said means connected between said substantially rigid backing and forwarding plate means comprises:

an end threaded bolt extending through said substantially rigid backing plate means, said encapsulated first washer, first, second, and third ring-shaped pi ezoelectric means, second washer means, and said substantially rigid forwarding plate means; and

a nut tightly screwed on the threaded end of said bolt.

22. The invention of claim 20, further characterized by:

a first compartment connected to the rear end of said substantially rigid backing plate means adapted for housing a predetermined electronic utilization apparatus that is electrically connected to the aforesaid electrical conductor means; and

a second compartment, having a substantially streamlined nose configuration, connected to the front of said substantially rigid forwarding plate means.

a is =0 is w 

1. An electroacoustical transducer, comprising in combination: a substantially rigid backing plate means, having at least one hole therethrough; first washer means, having a predetermined inside diameter and a predetermined outside diameter, spatially disposed from said substantially rigid backing plate means; a first ring-shaped piezoelectric means, having a first inside diameter and a first outside diameter, spatially disposed from said first washer means, for producing a first acoustical energy in proportional response to electrical energy supplied thereto and vice versa; a second ring-shaped piezoelectric means, having a second inside diameter that is different from the first inside diameter of said first ring-shaped piezoelectric means and a scond outside diameter that is similar to the first outside diameter of said first ring-shaped piezoelectric means, for producing a second acoustical energy in proportional response to electrical energy supplied thereto and vice versa; a third ring-shaped piezoelectric means, having a third inside diameter that is different from the first and second inside diameters of said first and second ring-shaped piezoelectric means and a third outside diameter that is similar to the first and second outside diameters of said first and second ringshaped piezoelectric means, for producing a third acoustical energy in proportional response to electrical energy supplied thereto and vice versa; a second washer means having a predetermined inside diameter and a predetermined outside diameter, spatially disposed from said third ring-shaped piezoelectric means; electrical conductor means connected to said first, second, and third ring-shaped piezoelectric means and effectively passing through said at least one hole in said substantially rigid backing plate means for effecting the electrical connection thereof in a predetermined electrical circuit arrangement; a plurality of polyurethane spacer means having inside diameters greater than the largest of the inside diameters of said first, second, and third ring-shaped piezoelectric means and outside diameters smaller than the outside diameters thereof respectively disposed between adjacent ones of said first, second and third ring-shaped piezoelectric means and the aforesaid first and second washer means; and acoustically clear means connected to each of the aforesaid means for effecting the holding thereof in the aforesaid spatial dispositions, respectively, for the containment thereof as an encapsulated unit of predetermined external geometrical configuration.
 2. The device of claim 1, wherein said substantially rigid backing plate is a circular metallic backing plate having a plurality of holes therethrough.
 3. The device of claim 1, wherein said substantially rigid backing plate is a circular aluminum backing plate having a plurality of holes therethrough.
 4. The device of claim 1, wherein said first washer means has an inside diameter that is similar to the inside diameter of said first ring-shaped piezoelectric means and an outside diameter that is greater than the outside diameter thereof.
 5. The device of claim 1, wherein said second ring-shaped piezoelectric means has an inside diameter that is greater than the inside diameter of said first ring-shaped piezoelectric means and has an outside diameter that is similar to the outside diameter thereof.
 6. The device of claim 1, wherein said first ring-shaped piezoelectric means has an inside diameter of 3.000 inches and an outside diameter of 3.100 inches.
 7. The device of claim 1, wherein said second ring-shaped piezoelectric means has an inside diameter of 2.900 inches and an outside diameter of 3.100 inches.
 8. The device of claim 1, wherein said third ring-shaped piezoelectric means has an inside diameter of 2.950 inches and an outside diameter of 3.100 inches.
 9. The device of claim 1, wherein the spaces between said first, second, and third spatially disposed ring-shaped piezoelectric means are each 0.032 inches.
 10. The device of claim 1, wherein said third ring-shaped piezoelectric means has an inside diameter that is smaller than the inside diameter of said second ring-shaped piezoelectric means and larger than the inside diameter of said first ring-shaped piezoelectric means and an outside diameter that is similar to the outside diameter of said first and second ring-shaped piezoelectric means.
 11. The device of claim 1, wherein each of said first, second, and third ring-shaped piezoelectric means comprises a lead zirconate-lead titanate ceramic ring and a pair of silver electrodes connected to opposite side surfaces thereof.
 12. The device of claim 1, wherein said second washer means has an inside diameter that is similar to the inside diameter of said third ring-shaped piezoelectric means and an outside diameter that is greater than the outside diameter thereof.
 13. The device of claim 1, wherein said acoustically clear means connected to each of the aforesaid means for effecting the holding thereof in the aforesaid spatial dispositions comprises a substantially resilient polyurethane material.
 14. The device of claim 1, wherein said electrical conductor means comprises: a pair of electrodes connected to opposite surface sides of each of said first, second, and third ring-shaped piezoelectric means; and a pair of electric wires respectively connected to each of the similar side electrodes of the pair of electrodes connected to opposite surface sides of each of said first, second, and third ring-shaped piezoelectric means for effecting the connection of said first, second, and third ring-shaped piezoelectric means in predetermined electrical circuit arrangement.
 15. The device of claim 14, wherein said predetermined electrical circuit arrangement is in electrical parallel.
 16. The device of claim 14, wherein said predetermined electrical circuit arrangement is in electrical series.
 17. The device of claim 14, wherein said predetermined electrical circuit arrangement is such that said first, second, and third ring-shaped piezoelectric means are connected in electrically independent arrangement.
 18. The device of claim 1, wherein said acoustically clear means connected to each of the aforesaid means for effecting the holding thereof in the aforesaid spatial disposition is further disposed in such manner as to encapsulate said first washer means, said first, second, and third ring-shaped piezoelectric means, said second washer means, and is connected to said substantially rigid backing plate means in such manner to be securely attached thereto as effectively an extension thereof.
 19. The invention of claim 18, further characterized by a substantially rigid forwarding plate disposed in abutment with that external surface portion of the aforesaid acoustically clear encapsulating means that is adjacent to said second washer means; and means connected between said substantially rigid backing and forwarding plate means for holding said encapsulated first washer means, first, second, and third ring-shaped piezoelectric means, and said second washer means therebetween.
 20. The invention of claim 19, wherein said means connected between said substantially rigid backing and forwarding plate means comprises at least one threaded bolt and a nut screwed on the end thereof.
 21. The invention of claim 19, wherein said means connected between said substantially rigid backing and forwarding plate means comprises: an end threaded bolt extending through said substantially rigid backing plate means, said encapsulated first washer, first, second, and third ring-shaped piezoelectric means, second washer means, and said substantially rigid forwarding plate means; and a nut tightly screwed on the threaded end of said bolt.
 22. The invention of claim 20, further characterized by: a first compartment connected to the rear end of said substantially rigid backing plate means adapted for housing a predetermined electronic utilization apparatus that is electrically connected to the aforesaid electrical conductor means; and a second compartment, having a substantially streamlined nose configuration, connected to the front of said substantially rigid forwarding plate means. 